Regional Stratigraphic Analysis of Cotton Valley Group of Upper Gulf Coastal Plain

Abstract

Lithologic and thickness data of Upper Jurassic rocks of the Cotton Valley group, Upper Gulf Coastal Plain, were interpreted from electric and sample logs, and selected correlations were carried from Arkansas and Louisiana into Texas, Mississippi, and Alabama. Units mapped include the total Cotton Valley, the Schuler formation, and the Bossier formation. Maps included are based on isopachs, lithofacies, shale ratios, and vertical variability. Sand in the Schuler is represented by a of map, a slice map of the top 1,000 feet, and a tripartite sand distribution map. The Bossier formation is a sequence of black shales and sands which may merge updip into a fringe of non-marine shale and sand. The Schuler formation oversteps the Bossier. The Schuler downdip aspect is predominantly marine. It thins updip through a transition zone of maximum shale percentage and maximum number of sands into a sequence of coarse clastic which may be an alternation of marine, deltaic, and continental sediments. It is believed that the Schuler formation was deposited on an unstable shelf flanking the Gulf Coast basin and receiving a supply of clastics from the north and northeast. The North Louisiana Interior Salt-Dome basin was separated from the East Texas basin by a shelf of less subsidence, an area referred to as the Sabine uplift. The marine sands of the Schuler formation presumably were deposited by longshore currents, carrying clastics westward from a major delta in northeastern Louisiana and western Mississippi. Facies patterns developed on all of the maps bear a definite relationship to the Cotton Valley producing trends in northern Louisiana.